Engine manufacturers and fuel suppliers continue to seek improved fuel economy and improved emission quality through engine design and formulating new fuels. There is pressure to minimize engine crank times and time from key-on to drive-away, while maintaining maximum fuel economy. Those pressures apply to engines fueled with alternative fuels such as ethanol as well as to those fueled with gasoline.
During cold temperature engine start, conventional spark ignition internal combustion engines are characterized by high hydrocarbon emissions, poor fuel ignition, and poor combustibility. Unless the engine is already at a high temperature after stop and hot-soak, the crank time may be excessive, or the engine may not start at all. At higher speeds and loads, the operating temperature increases and fuel atomization and mixing improve.
The worst emissions are during the first few minutes of engine operation, after which the catalyst and engine approach operating temperature. Regarding ethanol fueled vehicles, as the ethanol percentage fraction of the fuel increases to 100%, the ability to cold start becomes increasingly diminished, leading some engine manufacturers to include a dual fuel system in which engine start is fueled with conventional gasoline and engine running is fueled with the ethanol grade.